Runoff modeling in the High-Mountain River Basin: A Case Study of the Terek River (Caucasus, Russia)

Climate change and deglaciation in the 20th and 21st centuries cause runoff changes of a high-mountain regions. Modeling allows to predict runoff changes and possible extreme events in the future. In this research, we performed hydrometeorological data analysis, model calibration and validation in the key parts of the Terek River basin and simulated runoff and it’s components for a long-term historical period.

The Terek River flows from the highlands of the Central Caucasus and streams in an easterly direction, flowing into the Caspian Sea. Runoff modeling of the Terek River was carried out to the Mozdok outlet. The average height of the river basin is 1700 m, the basin area is 20600 km², of which 34% is the high-altitude part of the basin (>2000 m). A rise in both amount of water availability and potential natural hazard is characteristic of the North Caucasus that is considered to be caused by recent climate change. Mean annual runoff during 1978-2010 increased compared to 1945-1977 by 5-30 % in the foothills and by 30-70% in the plain area.

The ECOMAG runoff formation model (author Y. Motovilov) was adopted for the high-mountain part of the Terek River basin. The input data for the model are meteorological data (temperature, precipitation, air humidity deficit), soil and landscape information, and a digital elevation model, output modeling results – water discharges in a river network. In addition, the runoff formation model allows to analyze all components of water balance in different parts of a river basin and to divide the hydrographs by types of nutrition.

As a result, a long-term historical period from 1977 to 2018 was modeled. Due to the regional features of the river basin, an additional block of the model was included to account the glaciation. In addition to the daily runoff data, the separation of the flow into components in a key part of the river basin (the Baksan River) was used to validate the model. Based on the results of the calibration and verification of the model, a good agreement was obtained between the model and actual discharges for hydrological stations in the mountainous part of the basin. The NSE criterion for the 2009-2018 verification period was 0.75, the simulated and actual volumes of runoff differ by less than 10%.

The Terek River runoff formation model was developed under the financial support of RFBR 21-55-10003. Validation of the model based on the separation of the flow into components were designed within the framework of the Governmental Order to Water Problems Institute, Russian Academy of Sciences, subject no FMWZ-2022-0001.